A coupled bio-chemo-hydro-mechanical model for bio-cementation in porous media

Abstract

A key challenge involving microbially induced carbonate precipitation (MICP) is lack of rigorous yet practical theoretical models to predict the intricate biological–chemical–hydraulic–mechanical (BCHM) processes and the resulting bio-cement production. This paper presents a novel BCHM model based on multiphase, multispecies reactive transport approach in the framework of poroelasticity, aimed at achieving reasonable prediction of the produced bio-cement, and the enhanced geomechanical characteristics. The proposed model incorporates four key components: (i) coupling of hydro-mechanical stress–strain alterations with bio-chemical processes; (ii) stress–strain changes induced due to precipitation and growth of bio-cement within the porous matrix; (iii) spatiotemporal variability in hydraulic and stiffness characteristics of the treated medium; and (iv) velocity dependency of the attachment rate of bacteria. The fully coupled BCHM model predicts key unknown parameters during treatment including concentration of bacteria and chemical solutions, precipitated calcium carbonate, hydraulic properties of the solid skeleton, and in situ pore pressures and strains. The model was able to reasonably predict bio-cementation from two different laboratory column experiments. The Kozeny–Carman permeability equation is found to underestimate permeability reductions due to bio-cementation, while the Verma–Pruess relation could be more accurate. A sensitivity analysis revealed bio-cement distribution to be particularly sensitive to the attachment rate of bacteria.